One of the most common construction materials is pre-formed, hollow concrete or cinder block which is laid with masonry cement between the joints to build vertical walls. A particular problem in cold weather locations is maintaining the minimum temperature at which the cement mixture, which is a water-based compound, can be worked and dried. If the temperature is less than 32-degrees, an external heat source must be applied to raise the temperature of the cement so that the cement will not freeze and will set and dry in a short enough time to make the construction economically feasible. Prior art techniques of increasing the masonry temperature include heating the blocks and mixing the cement with hot water, and/or enclosing the entire work area with a temporary enclosure heated by a space heater. These measures are extremely expensive. Nonetheless, space heating is employed because of the even greater cost of delaying construction due to cold weather.
The most pertinent prior art patent of which the applicant is aware includes U.S. Pat. No. 3,729,614 issued on Apr. 24, 1973, entitled "Device for Accelerating the Setting of Concrete". This reference discloses means for heating and supplying water to a heating blanket which distributes the water in liquid or vapor form over the exterior surface of the concrete.
U.S. Pat. No. 2,592,578 issued on Apr. 15, 1952, entitled "Concrete Step Form", discloses a form for casting concrete steps which includes heating devices to apply heat to the outside of the concrete casting by locating heaters inside the form. U.S. Pat. No. 3,659,077 issued on Apr. 25, 1972, entitled "Apparatus for the Curing of Concrete", discloses the use of a layer of heat-conducting material carried by a frame in a position to overlie the upper surface of mixed concrete. The heat may be applied to a form or a flexible blanket that is placed over the exposed upper surface of the curing concrete mix. U.S. Pat. No. 5,419,059 entitled "Apparatus for Directing Pressurized Air Into A Wall or Ceiling for Drying Purposes Through An Electrical Box" issued on May 30, 1995 discloses the use of applying the inside of a wall damaged by water. However, none of the above-cited references teach or suggest the application of heat through passageways internal to the formed structure.